thr3ads.net - Rails - style question: "update or create" active record [Dec 2010]

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Fearless Fool

2010-Dec-07 19:25 UTC

style question: "update or create" active record

I find that I''m frequently writing code that could be described in
english as "If there is an incumbent ActiveRecord that meets some
specific criteria, then update one or more of its fields.  Otherwise
create a new record with the same criteria and new field values."

ActiveRecord''s dynamic finder methods (find_or_create_by_xxx) are not
usually expressive enough to do this.  But I haven''t been able to
create
a general method that smells right.  It''s been bugging me, so I turn to
the mavens of style in this forum for suggestions.

As an example, I just wrote this monstrosity:

  def set_xattribute(name, value)
    symbol_name = self.class.intern_symbol_name(name)
    incumbent = SymbolValue.
      where(:symbol_values => {:symbol_name_id => symbol_name.id}).
      where(:symbol_values => {:owner_id => self.id}).
      where(:symbol_values => {:xclass_id =>
self.class.xclass_id}).first
    if (incumbent)
      incumbent.update_attribute(:value, value)
    else
      SymbolValue.create(:symbol_name_id => symbol_name.id,
                         :owner_id => self.id,
                         :xclass_id => self.class.xclass_id,
                         :value => value)
    end
  end

Note the huge amount of repetition between the "finder" (incumbent
...) and the "creator" (SymbolValue.create(...)).  I can think of a
few
approaches to DRYing this code (e.g. scopes), but what do the mavens of
style in this forum suggest?

- ff

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Fearless Fool

2010-Dec-07 19:34 UTC

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style question: "update or create" active record

I find that I''m frequently writing code that could be described in
English as "If there is an incumbent ActiveRecord that meets some
specific criteria, then update one or more of its fields.  Otherwise
create a new record with the same criteria and new field values."

ActiveRecord''s dynamic finder methods (find_or_create_by_xxx) are not
usually expressive enough to do this.  But I haven''t been able to
create
a general method that smells right.  It''s been bugging me, so I turn to
the mavens of style in this forum for suggestions.

As an example, I just wrote this monstrosity:

def set_xattribute(name, v1, v2)
  symbol_name = self.class.intern_symbol_name(name)
  incumbent = SymbolValue.
    where(:symbol_values => {:symbol_name_id => symbol_name.id}).
    where(:symbol_values => {:owner_id => self.id}).
    where(:symbol_values => {:xclass_id => self.class.xclass_id}).first
  if (incumbent)
    incumbent.update_attributes(:v1 => v1, :v2 => v2)
  else
    SymbolValue.create(:symbol_name_id => symbol_name.id,
                       :owner_id => self.id,
                       :xclass_id => self.class.xclass_id,
                       :v1 => v1,
                       :v2 => v2)
  end
end

Note the code fragments repeated among the "finder" (incumbent = ...),
the "updater"  (update_attributes(...), and the "creator"
(SymbolValue.create(...)).  There may be a clever way to use scopes for
this, but what do the mavens of style in this forum suggest?

- ff

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Marnen Laibow-Koser

2010-Dec-07 19:40 UTC

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Re: style question: "update or create" active record

Fearless Fool wrote in post #966959:> I find that I''m frequently writing code that could be described in
> English as "If there is an incumbent ActiveRecord that meets some
> specific criteria, then update one or more of its fields.  Otherwise
> create a new record with the same criteria and new field values."
>
> ActiveRecord''s dynamic finder methods (find_or_create_by_xxx) are
not
> usually expressive enough to do this.
find_or_create_by_* will do exactly this.  You can specify additional 
fields for the "create" part of the action.  Please see the docs.

If that won''t do the trick, then please explain further.

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org

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Philip Hallstrom

2010-Dec-07 19:42 UTC

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Re: style question: "update or create" active record

On Dec 7, 2010, at 11:34 AM, Fearless Fool wrote:
> I find that I''m frequently writing code that could be described in
> English as "If there is an incumbent ActiveRecord that meets some
> specific criteria, then update one or more of its fields.  Otherwise
> create a new record with the same criteria and new field values."
> 
> ActiveRecord''s dynamic finder methods (find_or_create_by_xxx) are
not
> usually expressive enough to do this.  But I haven''t been able to
create
> a general method that smells right.  It''s been bugging me, so I
turn to
> the mavens of style in this forum for suggestions.
> 
> As an example, I just wrote this monstrosity:
> 
> def set_xattribute(name, v1, v2)
>  symbol_name = self.class.intern_symbol_name(name)
>  incumbent = SymbolValue.
>    where(:symbol_values => {:symbol_name_id => symbol_name.id}).
>    where(:symbol_values => {:owner_id => self.id}).
>    where(:symbol_values => {:xclass_id =>
self.class.xclass_id}).first
>  if (incumbent)
>    incumbent.update_attributes(:v1 => v1, :v2 => v2)
>  else
>    SymbolValue.create(:symbol_name_id => symbol_name.id,
>                       :owner_id => self.id,
>                       :xclass_id => self.class.xclass_id,
>                       :v1 => v1,
>                       :v2 => v2)
>  end
> end
> 
> Note the code fragments repeated among the "finder" (incumbent =
...),
> the "updater"  (update_attributes(...), and the
"creator"
> (SymbolValue.create(...)).  There may be a clever way to use scopes for
> this, but what do the mavens of style in this forum suggest?
You might play around with find_or_instantiator_by_attributes

http://apidock.com/rails/ActiveRecord/FinderMethods/find_or_instantiator_by_attributes

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Fearless Fool

2010-Dec-07 19:48 UTC

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Re: style question: "update or create" active record

BTW, the best I''ve come with so far is:

file: ar_extensions.rb
================class ActiveRecord::Base

  def self.create_or_update(attrs_to_match, attrs_to_update = {})
    if (incumbent = self.first(:conditions => attrs_to_match))
      incumbent.update_attributes(attrs_to_update)
      incumbent
    else
      self.create!(attrs_to_match.merge(attrs_to_update))
    end
  end

end
================... but maybe there is something more appropriate in the new
query
interface or AREL models?

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Fearless Fool

2010-Dec-07 20:39 UTC

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Re: style question: "update or create" active record

Marnen Laibow-Koser wrote in post #966963:> find_or_create_by_* will do exactly this.  You can specify additional
> fields for the "create" part of the action.  Please see the docs.
>
> If that won''t do the trick, then please explain further.
Hi Marnen:

Despite multiple re-reads of the documentation, I haven''t figured out
how to get it to update specific fields.  Maybe I''m just being dense.
Consider this AR class (slightly different than the example I gave, but
you''ll get the idea):
>> SymbolValue.first=> #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
owner_class_name_id: 1, value: "soso">

Let''s say I want to discriminate on :symbol_name_id, :owner_id and
:owner_class_name_id to select the record, and I want to update the
:value field.  Putting aside any complaints about the length of the
dynamic method name, here are two attempts that do NOT update :value:
>>SymbolValue.find_or_create_by_symbol_name_id_and_owner_id_and_owner_class_name_id(2,
1, 1, :value => "new_soso")
=> #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
owner_class_name_id: 1, value: "soso">
>>SymbolValue.find_or_create_by_symbol_name_id_and_owner_id_and_owner_class_name_id(2,
1, 1) {|s| s.value = "new_soso"}
=> #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
owner_class_name_id: 1, value: "soso">

As far as I can tell, the dynamic finder methods only set :value if a
new record is created, not if an existing record is found.  While that
may be useful, it''s not what I was asking for in the OP.

What am I missing?

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Marnen Laibow-Koser

2010-Dec-07 20:42 UTC

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Re: style question: "update or create" active record

Fearless Fool wrote in post #966995:> Marnen Laibow-Koser wrote in post #966963:
>> find_or_create_by_* will do exactly this.  You can specify additional
>> fields for the "create" part of the action.  Please see the
docs.
>>
>> If that won''t do the trick, then please explain further.
>
> Hi Marnen:
>
> Despite multiple re-reads of the documentation, I haven''t figured
out
> how to get it to update specific fields.  Maybe I''m just being
dense.
> Consider this AR class (slightly different than the example I gave, but
> you''ll get the idea):
>
>>> SymbolValue.first
> => #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
> owner_class_name_id: 1, value: "soso">
>
> Let''s say I want to discriminate on :symbol_name_id, :owner_id and
> :owner_class_name_id to select the record, and I want to update the
> :value field.  Putting aside any complaints about the length of the
> dynamic method name, here are two attempts that do NOT update :value:
>
>>>
> 
SymbolValue.find_or_create_by_symbol_name_id_and_owner_id_and_owner_class_name_id(2,> 1, 1, :value => "new_soso")
> => #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
> owner_class_name_id: 1, value: "soso">
>
>>>
> 
SymbolValue.find_or_create_by_symbol_name_id_and_owner_id_and_owner_class_name_id(2,> 1, 1) {|s| s.value = "new_soso"}
> => #<SymbolValue id: 1, symbol_name_id: 2, owner_id: 1,
> owner_class_name_id: 1, value: "soso">
>
> As far as I can tell, the dynamic finder methods only set :value if a
> new record is created, not if an existing record is found.  While that
> may be useful, it''s not what I was asking for in the OP.
Oh, I see now.  I misunderstood your original requirement.  Yeah, 
find_or_create_by_* won''t do that.

I think your create_or_update approach is reasonable.  Just don''t call 
the file ar_extensions; there''s already a plugin by that name.

>
> What am I missing?
Nothing, apparently. :)

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org

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Fearless Fool

2010-Dec-07 23:38 UTC

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Re: style question: "update or create" active record

Well, I couldn''t rest until I figured out an implementation of
create_or_update (see version 1 above) using the oh-so-nifty
ActiveRecord::Relation framework.

Here it is:

class ActiveRecord::Base

  def self.create_or_update(relation, attrs_to_update)
    if (incumbent = relation.first).nil?
      relation.create!(attrs_to_update)
    else
      incumbent.update_attributes(attrs_to_update)
      incumbent
    end
  end

end

What''s nice about this is that the relation can be a more expressive 
selector than a simple hash

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Rails - Dec 2010 - style question: "update or create" active record

style question: "update or create" active record

style question: "update or create" active record

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Re: style question: "update or create" active record

Re: style question: "update or create" active record

Re: style question: "update or create" active record

Re: style question: "update or create" active record

Re: style question: "update or create" active record